Elastic films are commonly incorporated into personal care articles to better shape the articles to the contours of the body. Elastic films can be used, for example, in the waist and leg areas of diapers, the side panels of training pants, and the cuffs of disposable gowns. It is common to apply one or more web layers, such as a nonwoven layer, to the elastic films to make them more textile-like. Typically, a nonwoven layer is joined to the elastic film in a stretched state. When the elastic film is allowed to recover, the nonwoven layer gathers, or shins, to create an extensible nonwoven laminate in the direction of stretch.
The processing of elastic films during the manufacture of extensible web laminates poses a number of challenges. For example, elastic films that are intrinsically stretchable in the machine direction (MD) are difficult to maintain under constant tension in a manufacturing line and are prone to premature stretching.
Additionally, elastic films tend to neck when stretched. When an elastic film is stretched in the MD, increased necking can lead to increased film width variability down web, resulting in process challenges for film alignment and uniform product construction. As a result, diaper manufacturers will purchase wider films to insure the width of the film does not drop below the desired dimensions during processing. The excess film or film-nonwoven laminate is then trimmed to produce a uniform product, a step that leads to trim waste and potentially increased web breaks and down time.
Necking also reduces the elasticity of the film, resulting in less efficient use of a relatively expensive component of personal care articles. If a nonwoven layer is bonded to the elastic film in the stretched state, the width of the elastic film will be confined by the nonwoven to the necked width. In other words, the elastic film is unable to relax to its original width, resulting in an overall loss of elasticity.
Efforts have been made to reduce the amount of necking in elastic films during processing. For example, necking can be minimized by shortening the gap distance between sequential differential speed rolls during MD stretch. However, such a modification imparts greater stress on the elastic film, resulting in more web breaks, rejected products and/or process down time.
Another attempt to minimize necking involves a multilayer film comprising at least one elastomeric layer and at least one relatively nonelastomeric skin layer. The multilayer film is activated via MD stretching, preferably through a spatially modified activation method such as disclosed in U.S. Pat. No. 5,344,691, “Spatially Modified Elastic Laminates,” (Hanschen, et al.). Once activated, the film exhibits less necking when subsequently stretched in the MD. However, as already mentioned above, films that are intrinsically stretchable in the MD have their own processing challenges (i.e. difficulty maintaining the film under constant tension in a manufacturing line and premature stretching).
Therefore, a need exists for a method of making extensible web laminates that makes efficient use of the elasticity of the film, minimizes film waste, and improves process handling capabilities of the film.